Fig. 1. Fluorescence microscopy of postmitotic C2C12 myocytes, infected with recombinant adenovirus, AdGFP-MHC, reveals the distribution of the expressed GFP-myosin. (A,B) GFP-myosin expression is readily apparent within 18-24 hours of infection. The GFP-myosin first appears in either fluorescent globular foci (A) or short filamentous structures (B). These globular and filamentous myosin intermediates are found distributed throughout the cytoplasm of young multi-nucleated syncitia as well as mono-nucleated myocytes. (C) As the differentiation of the C2C12 cells proceeds, large multinucleated myotubes develop (72-120 hours post infection) and the distribution of the GFP-myosin shifts to a pattern characteristic of striated myofibrils.